1. Field of the Invention
The disclosure relates generally to medical fluid delivery applications and, particularly, to a fluid delivery system including a high pressure sensor for measuring intravascular pressure of a patient during medical fluid delivery applications.
2. Description of Related Art
In many medical diagnostic and therapeutic procedures, a medical practitioner, such as a physician, injects a patient with a fluid. In recent years, a number of injector-actuated syringes and powered fluid injectors for pressurized injection of fluids, such as contrast media (often referred to simply as “contrast”), have been developed for use in procedures such as angiography, computed tomography, ultrasound, and NMR/MRI. In general, these powered fluid injectors are designed to deliver a preset amount of contrast at a preset flow rate.
Angiography is used in the detection and treatment of abnormalities or restrictions in blood vessels. In an angiographic procedure, a radiographic image of a vascular structure is obtained through the use of a radiographic contrast that is injected through a catheter. The vascular structures in fluid connection with the vein or artery in which the contrast is injected are filled with contrast. X-rays passing through the region of interest are absorbed by the contrast, causing a radiographic outline or image of blood vessels containing the contrast. The resulting images can be displayed on, for example, a video monitor and recorded.
In a typical angiographic procedure, the medical practitioner places a cardiac catheter into a vein or artery. The catheter is connected to either a manual or an automatic contrast injection mechanism. A typical manual contrast injection mechanism includes a syringe in fluid connection with a catheter connection. The fluid path also includes, for example, a source of contrast, a source of flushing fluid, typically saline, and a pressure transducer to measure patient blood pressure. In a typical system, the source of contrast is connected to the fluid path via a valve, for example, a three-way stopcock. The source of saline and the pressure transducer may also be connected to the fluid path via additional valves, again, such as stopcocks. The operator of the manual contrast injection mechanism controls the syringe and each of the valves to draw saline or contrast into the syringe and to inject the contrast or saline into the patient through the catheter connection. The operator of the syringe may adjust the flow rate and volume of injection by altering the force applied to the plunger of the syringe. Thus, manual sources of fluid pressure and flow used in medical applications, such as syringes and manifolds, typically require operator effort that provides feedback of the fluid pressure/flow generated to the operator. The feedback is desirable, but the operator effort often leads to fatigue. Thus, fluid pressure and flow may vary depending on the operator's strength and technique.
Automatic contrast injection mechanisms typically include a syringe connected to a powered fluid injector having, for example, a powered linear actuator. Typically, an operator enters settings into an electronic control system of the powered fluid injector for a fixed volume of contrast and a fixed rate of injection. In many systems, there is no interactive control between the operator and the powered fluid injector, except to start or stop the injection. A change in flow rate in such systems occurs by stopping the machine and resetting the injection parameters. Automation of angiographic procedures using powered fluid injectors is discussed, for example, in U.S. Pat. Nos. 5,460,609; 5,573,515; and 5,800,397.
The pressure transducer in the above-discussed modalities is used to provide a hemodynamic waveform, referred to as intra-coronary blood pressure, of a patient during clinical procedures. Cardiologists often refer to hemodynamic waveforms since they essentially provide real time measurement of blood pressure, which correlates to the performance of the heart. However, these pressure transducers are extremely sensitive to even moderate pressures generated during activation of the syringe, and many pressure transducers can be damaged if they are subjected to pressures as low as about 75 psi. Hand-held syringes can generate pressures of 200 psi or more. Power injectors may pressurize the contents of a syringe to pressure exceeding 1200 psi (about 63,000 mm Hg), far beyond the maximum pressure of the pressure transducer.
In view of these high pressure levels in existing fluid delivery systems, the systems include a means, such as a valve, for isolating the pressure transducer from the pressurized fluid in order to avoid damaging the pressure transducer during injection. While the syringe is not activated, the valve is open so that the pressure transducer can monitor blood pressure. In one known arrangement, the pressure transducer and contrast injection mechanism are connected to the catheter through a manifold. The manifold includes a manually operated valve that enables the injector operator to isolate the pressure transducer during the injection of the contrast solution. This valve, typically a stopcock, is used to isolate the pressure transducer to prevent damage thereto. Specifically, a stopcock configuration is provided which either allows the pressure transducer to be in fluid communication with the catheter or the injection mechanism to be in fluid communication with the catheter, but not both. Typically, the stopcock handle must be turned manually to switch between the two positions. Accordingly, this configuration provided by some currently available manifolds does not allow, for example, contrast injections to be made while the pressure transducer is in communication with the catheter.
Another pressure isolation valve used for pressure transducer protection purposes is disclosed by U.S. Patent Application Publication No. 2006/0180202 to Wilson, et al. This publication discloses an elastomeric valve having a valve body with three ports including a contrast inlet port, a saline inlet and pressure transducer port, and a patient or outlet port. The valve body houses a disc holder and a valve disc therein. The valve disc is formed from a molded elastomer, such as silicone rubber, with a slit in the center. The elastomeric disc is sandwiched between the valve body and disc holder and is affixed therebetween at the perimeter of the disc. Such affixation may be effected by entrapment, adhesion, mechanical, or chemical welding. The elastomeric valve disclosed by this publication is responsive to pressure changes in the valve that act on the elastomeric disc, and the elastomeric disc is operative to protect a pressure transducer connected to the pressure isolation port.
Fluid delivery systems having pressure isolation valves that open and close automatically are also known in the art. For example, U.S. Pat. No. 7,610,936 to Spohn, et al., incorporated herein by reference, discloses a fluid delivery system having a pressure isolation mechanism that includes a flow-activated valve member adapted to selectively engage a seal seat to establish fluid isolation between a fluid delivery system and a pressure transducer. The flow-activated valve member is responsive to increased fluid flow through a fluid path connected to the pressure isolation mechanism and the valve member is operable to engage and seal against an opposing seal seat. The valve member movement effectively closes-off fluid flow to a port to which a pressure transducer is connected, thereby isolating the pressure transducer when high pressure fluid is injected through the fluid path.
However, despite the fact the above-described valves effectively protect and isolate a pressure transducer when used correctly, there are a number of drawbacks to such active pressure isolation valve mechanisms. First, with manual isolation valves, the user may forget to close the valve before activating the associated syringe, and the pressurized fluid flow through the system will likely damage the transducer. Additionally, if the valve is not closed correctly, there is a risk that fluid drainage would occur through the valve or port, during pressure transducer zeroing. Furthermore, automatic or active pressure isolation valves often rely on sealing, locking, or release mechanisms which tend to be complex and, in some cases, prone to breaking or becoming stuck in an open or closed position, or have a tendency to trap air.
Additionally, known pressure sensors must be positioned in a separate port, typically a branch port, a secondary fluid path, or line from the main fluid path of a fluid delivery system. While the branch port or the secondary fluid path is selectively in fluid communication with the main fluid path, the branch or delta between the pressure sensor and the main fluid path reduces the accuracy and reliability of pressure measurements. Furthermore, each branch of a fluid system must be primed with a fluid, such as saline, during use. In systems in which the pressure sensor is included in a branch, port, or secondary fluid path, which is separate from the main fluid path, a user must perform an extra flushing activity on the branch, port, or secondary fluid path leading to the pressure sensor, and these locations are prime locations for trapping air bubbles. Performing an additional flushing activity increases the difficulty and time required to perform a fluid injection.